Apparatus for crucible-free zone melting with a vacuum chamber



R. EMEIS July 2. 1968 APPARATUS FOR CRUCIBLE-FREE ZONE MELTING WITH A VACUUM CHAMBER File d Oct. 22, 1965 8 5 1 1 9 3 m J I In g United States Patent O 3,391,235 APPARATUS FOR CRUCIllLE-FREE ZONE MELTING WITH A VACUUM CHAMBER Reimer Emeis, Ebermannstadt, Germany, assignor to Siemens Aktiengesellschaft, a corporation of Germany Filed Oct. 22, 1965, Ser. No. 501,674 Claims priority, applicgtigfinsfigrmany, Apr. 28, 1965,

5 Claims. (c1. 13-1 My invention relates to apparatus for crucible-free zone melting with a vacuum chamber.

Apparatus for crucible-free zone melting with a vacuum chamber having holders by means of which the rodshaped material to be processed is held in a vertical posi tion and further having heating means located in the vacuum chamber and actuable from outside the chamber so as to be displaceable vertically upward and downward, have heretofore become known. With the aid of the heating device a melting zone is produced in the rod-shaped material and is passed by relative motion between the rod-shaped material and the heating device over the entire length of the rod-shaped material. For this purpose, either the heating device or the rod can be displaceable in a vertical direction. The rod holders are preferably rotatable about the vertical axis so as to achieve a uniform cross section. The size of the rod cross section can be kept uniform by moving the rod holders toward and away from one another in response to optical or electrical measurement values, for example, whereby the melting zone is respectively thickened or stretched, i.e. compressed or elongated respectively, so that the material crysallizing out of the melting zone has a respective enlarged or reduced cross section.

The problem of supplying current to the moving electrical heating device and simultaneously moving the heating device has been solved in accordance with US. Patent No. 2,904,663, wherein a plurality of electrically conductive tubes of varying width located coaxially within one another carry the heating device as well as conduct current thereto, the conducting tube with the greatest width extending through a wall, preferably the base of the vacuum vessel, i.e. through an apertured gas-tight fitting located in the wall, and is displaceable in its longitudinal direction. The solution provided by the apparatus of the aforementioned patent has the advantage that the holder of the heating device, the current leads to the heating device, and, if necessary, a coolant loop for the heating device, can be combined together so that only one apertured fitting in the wall of the vacuum vessel is necessary for this operating equipment.

'It has been found, however, that when the apertured insert is located in the base or roof of the vacuum vessel, some difficplty is presented in the manipulation of the holder for the heating device and its associated leads and coolant loops. Also, due to the location of the insert at the bottom or top of the vacuum vessel, the current leads to the heating device through the heating device holder have had to be rather lengthy thereby resulting in substantial electrical losses, particularly when the electrical heating device is in the form of an induction heating coil. In such a case, generally, the induction heating coil is connected in parallel with a capacitance comprising a bank of condensers forming a resonant heating circuit with the induction heating coil that is energized by a high frequency generator. If the spacing between the capacitance and the inductance of this heating circuit is relatively large, which can be the case for semiconductor rod material being processed having a very great length, the losses in the heating circuit will then be disproportionately large.

It is accordingly an object of my invention to avoid the foregoing disadvantages of the known devices and to pro- 3,391,235 Patented July 2, 1968 vide apparatus for crucible-free zone melting with a vacuum chamber wherein the holder for the heating device will extend through an apertured fitting located in a side wall of the vacuum vessel so thatit is more easily manipulatable.

It is a further object of my invention to provide such an apparatus which will reduce the electrical losses caused by the passage of the current over a long path before reaching the heating device.

With the foregoing and other objects in view, I provide in accordance with my invention apparatus for cruciblefree zone melting comprising a vacuum chamber, holders mounted in the chamber for holding the rod-shaped material to be processed in a vertical position, and a heating device mounted so as to be displaceable in the vacuum chamber in a vertical direction and movable from outside the vacuum chamber. In accordance with a specific feature of the invention, a vertically extending slot is formed in a side wall of the vacuum chamber and is covered by a plate which is displaceable in a vertical direction and a holder for the heating device extending through the slot and secured to the plate.

In accordance with another feature of my invention, the spacing between the current leads to the electrical heating device, that are located outside the vacuum chamber, and the heating device proper is consequently always relatively small and independent of the rod length of the material that is being processed. The mechanical stability of the holder of the heating device is thereby also promoted.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in apparatus for crucible-free zone melting with a vacuum chamber, it is nevertheless not in tended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of a specific embodiment when read in connection with the accompanying drawings, in which:

FIG. 1 is a vertical sectional view of a zone melting apparatus constructed in accordance with my invention;

FIG. 2 is a cross sectional view of FIG. 1 taken along the line II--II in the direction of the arrows; and

FIG. 3 is a right-hand side view of FIG. 1 with the outer plate and heating coil holder removed, showing details of the seal for the slot formed in the side wall of the vacuum vessel.

Referring now to the drawings, there is shown a zone melting apparatus having a box-shaped housing 2 which can consist, for example, of steel. A door 3 is located in a side wall of the vacuum chamber which will accordingly be referred to herein as the front wall of the zone melting apparatus. In the door 3 there is located a window 4 which can, for example, consist of bullet-proof glass. For the sake of clarity and simplicity in the drawing, the necessary seals for the glass window 4 in the door 3 have been omitted. The material to be processed is in the form of a rod 5 located within the vacuum vessel, and can, for example, consist of a semiconductor rod of silicon. The rod 5 is held between two holders 6 and 7 which can be moved with the aid of the shafts 8 and 8' from outside the vacuum vessel. Thus, for example, the holder 7 can be rotated about its axis as indicated by the curved arrow associated therewith whereas the other holder 6 can be moved up and back vertically, as indicated by the double-headed arrow associated therewith, and can accordingly perform the aforedescribed stretching and compressing motion for equalizing or varying the cross section of the material being processed. Of course, both holders 6 and 7 can be simultaneously rotated and/ or displaced in a vertical direction, as viewed in FIG. 1. With the aid of an electrical heating device 9, for example an induction heating coil, a melting zone 10 can be produced in the rod 5. This heating can also be accomplished by any suitable radiation heating device.

In one of the side walls of the vacuum vessel 2 i.e. the wall located behind the plane of the drawing of FIG. 1, there is located a connecting conduit 11 by the aid of which the interior of the vacuum chamber 2 can be evacuated. In another side wall, referred to hereinafter as the rear wall and located at the right-hand side of FIG. 1 and opposite to the front wall containing the viewing window 4 through which supervising personnel can see the rear wall, there is formed a vertical slot 12. The slot 12 is covered by a plate 13 serving to seal off the slot from the surrounding air. A holder 14 for the heating device 9 is secured to this plate 13. The holder 14 preferably extends vacuum-tightly through the plate 13 so that it can serve simultaneously as the conductive supply line for the current and, if necessary, as means for supplying coolant such as cool water through a cooling loop therein. For further details of such a holder, reference can be made to the copending application Ser. No. 363, 339, of W. Keller et a1. filed Apr. 24, 1964. The holder 14 extends with clearance through the slot 12 permitting the holder 14 and therewith also the heating device 9 to be displaced with the plate 13 in a vertical direction. The plate 13 is made longer than the slot 12 so that the slot always remains covered when the plate 13 is moved vertically. The rear wall of the vacuum chamber shown at the right-hand side in FIG. 1 and the plate 13 are accommodated to one another, for example by grinding and polishing so that an effective sealing of the slot 12 is assured. An intermediate member can also be provided which can be sealingly placed on the exterior of the vacuum chamber 2 surrounding the slot 12, and the plate 13 can be located thereon for displacement in a vertical direction. The production and machining of the sliding surfaces for the plate 13 are thereby greatly facilitated.

A groove 15 is additionally provided in the rear wall completely surrounding the slot 12 and filled with a sealing liquid such as oil for example. When so-called vacuu-m oil, which has a very low vapor pressure, is used, the inner space of the vacuum chamber can be safely sealed from the outer air. Furthermore, by suitable cooling the vapor pressure can be maintained at a low value. An equalizing vessel 16 is preferably provided for replacing the oil loss in the groove 15 and serves simultaneously for equalizing heat expansion of the sealing liquid. At the lower end of the plate 13, as viewed in FIG. 1, there is provided a collecting groove or vessel 17 for receiving the liquid sealant which may run or flow down the plate 13. The oil in the groove 15 is under outer atmospheric pressure (1 at), so that in a disadvantageous case some of the oil will reach into the vacuum vessel.

A further improvement can accordingly be effected by providing a second groove 18 in the rear wall which also completely surrounds the slot 12 and which is located between the slot and the groove 15 that is filled with sealant liquid. A vacuum pump with a pre-vacuum is necessary to produce a high vacuum in the chamber of the apparatus; in this case the groove 18 can be connected to the pre-vacuum so that, if necessary, sealant liquid originating from the groove 15 can be drained into the pre-vacuum before reaching the slot 12. The difiicult problem of the sealing can thus be solved.

In FIG. 3 the rear wall of the vacuum chamber is shown with the plate 13 removed; the separate grooves 15 and 18 surrounding the slot 12 are clearly illustrated therein.

When induction heating of the melting zone 10 is provided, the capacitors (not shown) connected in parallel to the induction heating coil 9 are mounted in a housing 19 which is secured directly to the plate 13 at a location thereof through which the holder 14 extends. When the capacitors are water-cooled (from 2000 to 3000 pf. at 2 kv. and 4 mHz. frequency) it is very difii-cult to locate these capacitors inside the vacuum chamber 2, so that the inventive solution of this application avoids this dirliculty. As can be seen from FIGS. 1 and 2, the spacing between the induction heating coil 9 and the capacitor group or bank 19 is relatively small so that the losses from the holder 14 which acts as current conducting lead can also be kept very small whereas the inductance of the current connecting lead between the heating coil 9 and capacitance 19 for a different arrangement and thereby for a necessarily greater spacing in spite of the coaxial arrangement can have the order of magnitude of the inductance of the heating coil 9. The electrical leads from a high-frequency generator and the coolant loop conduits can be readily inserted from the outside of the vacuum vessel, as clearly evident from the drawing and the disclosure herein.

I claim:

1. Apparatus for crucible-free zone melting rod-shaped material comprising a vacuum chamber having a side wall, holding means mounted in said chamber for holding the rod-shaped material in a substantially vertical position, heating means located in said chamber for heating the rod-shaped material to form a melting zone therein, the side wall of said chamber being formed with a substantially vertically extending slot, a plate adjacent said side wall outside of said chamber for covering and her metically sealing said slot, said plate being displaceable from outside said chamber in a substantially vertical direction, and holder means for said heating means extending from said chamber through said slot and secured to said plate whereby said heating means may be vertically displaced with said plate for passing the molten zone vertically through the rod-shaped material.

2. Apparatus according to claim 1 wherein a groove is formed in said side wall and completely surrounds said slot, said groove being filled with a sealing fluid and being completely covered by said displaceable plate.

3. Apparatus according to claim 2 including a supply vessel for sealing fluid located above and communicating with said groove.

4. Apparatus according to claim 2 including a second groove formed in said side wall and completely surrounding said slot, said second groove being located between said slot and said first-mentioned groove.

5. Apparatus according to claim 2, wherein said heating means is an electric heating device and said holder means therefor is formed as a current supply line.

References Cited UNITED STATES PATENTS 2,937,216 5/1960 Fritts et -al. 13-1 3,270,177 8/1966 Prediger et al l31 X BERNARD A. GILHEANY, Primary Examiner.

R. N. ENVALL, ]R., Assistant Examiner. 

1. APPARATUS FOR CRUCIBLE-FREE ZONE MELTING ROD-SHAPED MATERIAL COMPRISING A VACUUM CHAMBER HAVING A SIDE WALL, HOLDING MEANS MOUNTED IN SAID CHAMBER FOR HOLDING THE ROD-SHAPED MATERIAL IN A SUBSTANTIALLY VERTICAL POSITION, HEATING MEANS LOCATED IN SAID CHAMBER FOR HEATING THE ROD-SHAPED MATERIAL TO FORM A MELTING ZONE THEREIN, THE SIDE WALL OF SAID CHAMBER BEING FORMED WITH A SUBSTANTIALLY VERTICALLY EXTENDING SLOT, A PLATE ADJACENT SAID SIDE WALL OUTSIDE OF SAID CHAMBER FOR COVERING AND HERMETICALLY SEALING SAID SLOT, SAID PLATE BEING DISPLACEABLE FROM OUTSIDE SAID CHAMBER IN A SUBSTANTIALLY VERTICAL DIRECTION, AND HOLDER MEANS FOR SAID HEATING MEANS EXTENDING FROM SAID CHAMBER THROUGH SAID SLOT AND SECURED TO SAID PLATE WHEREBY SAID HEATING MEANS MAY BE VERTICALLY DISPLACED WITH SAID PLATE FOR PASSING THE MOLTEN ZONE VERTICALLY THROUGH THE ROD-SHAPED MATERIAL. 